rpmdb: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/rpmdb - from package: rpm

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/rpmdb - from package: rpm

You may install the required package with command apt-get install {package}

Error in other languages:
rpmdb: bevel nie gevind nie
rpmdb: comandă negăsită
rpmdb: comando não encontrado
rpmdb: commande introuvable
rpmdb: command not found
rpmdb: käsku ei ole
rpmdb: không tìm thấy lệnh
rpmdb: komanda nerasta
rpmdb: Kommando nicht gefunden.
rpmdb: kommandot finns inte
rpmdb: komut yok
rpmdb: nie znaleziono polecenia
rpmdb: níor aimsíodh an t-ordú
rpmdb: no se encontró la orden
rpmdb: no s'ha trobat l'ordre
rpmdb: opdracht niet gevonden
rpmdb: parancs nem található
rpmdb: perintah tidak ditemukan
rpmdb: príkaz nenájdený
rpmdb: příkaz nenalezen
rpmdb: команда не найдена
rpmdb: командата не е открита
rpmdb: 命令找不到
rpmdb: コマンドが見つかりません